(1) Field of the Invention
The present invention relates to a duplex printing apparatus and a control method of the same apparatus suitable for performing electrophotographic printing on the obverse and reverse sides of continuous recording paper by a plurality of image forming sections and fixing sections provided within a single apparatus.
(2) Description of the Related Art
There is a conventional duplex printing apparatus that performs printing on both the obverse and reverse sides of a recording medium such as continuous recording paper (hereinafter referred to as a medium) by an electrophotographic method. Within the apparatus, the medium is conveyed. At a position opposite to one side of this medium, a first image forming process section for forming a toner image on the one side of the medium is disposed. At a position opposite to the other side of the medium and also downstream from the first image forming process section, a second image forming process section for forming a toner image on the other side of the medium is disposed. Furthermore, fixing sections for fixing the toner images formed on both sides of the medium are disposed. When the medium is being conveyed within the printing apparatus, printing is performed on both sides of the medium in sequence.
However, in such a conventional duplex printing apparatus, in making a switch-over from one printing mode to another printing mode for example, from a one-side printing mode for printing on only one side (e.g., obverse side) of a medium with the second image forming process section to another one-side printing mode for printing on only the other side (e.g., reverse side) of the medium with the first image forming process section, or to a double-side printing mode for printing on both the observe and reverse sides of the medium with the first and second image forming process sections, the last line position of the toner image, formed by the second image forming process section, is located at a position on the medium downstream from the printing start position of the first image forming process section, when one printing mode ends. For this reason, in this state, if printing is started in another printing mode and image formation is started by the first image processing unit, there is a problem that the portion of the medium between the first and second image forming process sections will become wasted.
Also, to exclude such a wasteful portion of the medium between the first and second image forming process sections, it is considered that the last end portion of the unfixed toner image, formed by the second image forming process section, is fed back to the printing start position of the first image forming process section in the opposite direction from the conveying direction for printing. In this case, when the last end position of the unfixed toner image on the medium, formed by the second image forming process section, is fed back to the printing start position of the first image forming process section, there is a problem that the unfixed toner image, formed on the medium between the second image forming process and the fixing section, will be disturbed by contact with the image forming drum of the second image forming process section and therefore the printing quality will be reduced.